Bore sighting device



vNOV. 6, 1951 A L C, GARDNER 2,573,703

BORESIGHTING DEVICE Filed Nov. '10, 1949 v zAsr-lEETs-SHEET 2 uIrviT-ua- E- Ear'cfner' Patented Nov. 6, 1951 BORE SIGHTING DEVICE Irvine C. Gardner, Chevy Chase, Md., assigner to the United States of America as represented by the Secretary of the Army Application November 10, 1949, Serial No. 126,663

(Granted under the act of March 3, 1883, -as amended April 30, 1928; 370 0. G. 757) Claims.

vThe invention described in this specification and claims may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty there- The present, invention relates to an optical system for boresighting artillery pieces and is particularly adapted for employment in those situations where it is not practicable to erect or select suitable objects the requisite distance in front of an artillery piece for such purpose by any of the conventional procedures.

To accurately direct an artillery piece upon a target it is necessary, as is well understood in the art, that the line of sight of the optical sighting system and the axis of the bore of the piece be parallel. At present this is usually accomplished by erecting a panel at a considerable distance in front of the artillery piece and substantially normal to its axis. This panel bears two targets spaced horizontally and vertically by the same distance as the axes of the bore of the piece and of the optical sight mounted on the carriage of the piece. The axis of the bore of the piece is established by a suitable method such as by inserting diaphragms in the bore of the piece having cross hairs adjacent the muzzle and a peep hole adjacent the breech, both of which are centered on the bore axis. The piece isthen trained by sighting through the peep hole to bring the cross hairs upon the target corresponding to the axis of the piece which is borne by the panel. If the axis of the optical sight is parallel to thel axis of the gun it will then be directed upon the target borne by the panel corresponding to the optical axis of the sight mounted upon the carriage of the piece. If the axes of the vbore of the piece\`and optical sight are parallel both will be directed to coincide with their respective targets upon the panel, but if this condition does not obtain appropriate adjustments are made to eiect such condition.

In utilizing the conventional system just outlined, it is necessary that the panel bearing the targets be set up at a considerable distance in front .of the piece as the optical sight is often not provided with means for'focussing and if the panel is too close excessive parallax will render the method inaccurate. Further, the closer to the piece that the panel is located the greater will be the resulting error from any inaccuracy in establishing the targets upon the panel.

The principal object of my invention is to provide an optical bore sighting system which will obviate the disadvantages inherent in the conventional system just described.

A further object of my invention is to provide a compact boresighting system embodied in a device that is generally encompassed within the profile of an artillery piece to which it is adapted to be attached and which is operable to accurately boresight the piece without the use of instruments or aids not contained within the system.

With these and other objects in View the following is a specification of one embodiment of the invention wherein;

Figure 1 is a horizontal sectional view of the boresight showing a horizontal sectional muzzle portion of an artillery piece unto which it is attached and a plan view of the telescopic sight of the piece in relative position to the boresight;

Figure 2 is a sectional view upon the line 2-2 vof Figure l; Figure 3 is an elevation of the collimator portion of the boresight which coacts with the telescopic sight of the artillery piece;

Figures 4 and 5 are sectional views taken upon the lines 4-4 and 5-5 of Figure 1;

Figure 6 is a view showing a modification of securing the diaphragms of the boresight in the bore of an artillery piece;

Figure 7 is a sectional view taken upon the line 1-1 of Figure 6.

Referring to the drawings by means of reference characters it will be seen that the boresight system is generally indicated at IIJ and is comprised of a collimator II, carried by spaced diaphragms I2 and I3 inserted within the bore of the muzzle portion I4 of an artillery piece equipped with a telescopic sight I5. A supporting structure or chassis indicated at I6 is attached to the muzzle of the piece by means of a collar I'I affixed to the chassis in any appropriate manner and a suitable clamp I8 A actuatable by any conventional means for such purpose as by the bolt I9. The |chassis I6 has mounted thereupon a penta-prism 20 adapted to deviate light emanating from the collimator II through as shown. Upon the end portion of chassis I6 remote from the pentaprism 20 there is mounted another penta-prism 2| adapted to deviate light rays from pentaprism 20 through 90 for the purpose of directing such rays into the telescopic sight I5. An extension 22 of the chassis I6 has trunnioned thereupon a second collimator 23 located in proper relative relation to telescopic sight I5, collimator 23 being adjustable in a vertical plane by means of adjusting screw 24.

I The collimator II and diaphragms I2--I3 may be formed as a unit with the diaphragms machined or otherwise iinished to tolerances to accurately t the bore of any particular artillery piece, so that the line of collimation of collimator II coincides with the axis of the bore of the piece or is parallel with such other reference line that it may be desired to establish through the bore of the piece. It is of course apparent that the accuracy of alignment of the line of collimation with respect to a selected reference line of the bore of the piece may be increased by increasing the distance between diaphragms I2-I3 and by inserting the diaphragms in portions of the bore of the piece selected to be least aected by ero'- sion of the piece due to firing.

If preferred, instead of providing the diaphragms I2--I3 with tolerances adapting them to accurately t the bore, modied diaphragms such as diaphragm shown in Figure 6 may be employed In this form of diaphragm three or more expanding shoes 26 are slidably mounted upon the diaphragm and adapted to be radially' ex- -panded into contact with the surface of the bore of the piece by cams 21 borne by a cam plate 28 which is rotatably mounted in the diaphragm 25 ,and rotatable as by means of the pinion 29 .mounted on the diaphragm and gear sector 30 attached to the cam plate. The pinion 29 may be vrotated through any suitable device such as the vtioned to permit retraction of the shoes.

The penta-prisms 20--2I should be so selected that their combined deviation does not impart from 180 more than the allowable error in boresighting. For example if an inaccuracy of 0.1 mil is chosen to be the maximum allowable boresighting error each of the prisms must deviate light 90 I10 seconds, which is a very generous allowable error for penta-prisms. In practice the penta-prisms need not be large, a clear aperture of 3A normally suflicing, consequently the size of the prisms can be kept within limits which will obviate deviations caused by temperature gradients or mechanical strains arising in prisms of larger size.

As more particularly shown in Figure 1 the face 32 of penta-prism 2| is half silvered, and a prism 33, so shaped as to permit light to be transmitted through the composite unit formed by prisms 2I-33 as a plane parallel plate, is cemented to the face 32 of prism 2|.

The collimators I I and 23 will be satisfactory in almost all cases if they are designed to have a free aperture of 1/2 inch for the objectives thereof. The reticle in the focal plane of the objective of collimator II comprising a single diametral line or other appropriate indicia 34 which is oriented to be normal to the plane containing the axes of the artillery piece and the telescopic sight of the piece, while the reticle in collimator 23 comprises a single diametral line or other appropriate indicia 35 adapted to be oriented in the plane of or a plane parallel to a horizontal plane containing the axis of the bore of the piece. The reticles of collimators II and 23 may be illuminated by lamps 35 as is well understood in the art. As indicated in Figure 3 the collimator 23 is provided with surfaces 31-38 which are accurately parallel to the line of collimation of the collimator whereby the inclination or elevation of collimator 23 may be adjusted by means of a gunners quadrant seated upon these surfaces.

In operation the lamps 36 will illuminate the reticles of collimators II and 23. Light from colr limator II will impinge upon penta-prism 20 and be deviated whereupon it will then impinge upon penta-prism 2l and again be deviated 90 to enter telescopic sight I5 where an observer will be enabled to view the diametral line 34 of collimatorY Il. Light from collimator 23 will impinge upon prism 33 and be transmitted through prisms 33-2I without deviation as in transmission through a plate having plane parallel surfaces and enter telescopic sight I5 enabling the observer to view diametral line 35. If the axes of the telescopic sight and bore of the piece are parallel in azimuth the line 34 of collimator I I and line 35 of collimator 23 will appear to be superposed in intersecting relationship upon the ducial mark of the telescopic sight reticle. In the event that this is not the case the coincidence desired can be attained by making appropriate adjustment of the telescopic sight axis to bring it into parallelism with the bore axis of the piece.

The collimator 23 is trunnioned so as to be adjustable in the vertical plane by 'means of the screw 24. By determining the elevation of the piece by a gunners quadrant the collimator may be adjusted to the same elevation by resting the gunners quadrant upon the surfaces 38 of the collimator and adjusting screw 24 until the elevation desired is obtained. While boresighting will normally be accomplished at zero elevation of the bore of the piece, if this lis not practicable correct boresighting can be accomplished by adjusting the collimator and piece to the same elevation.

Although Figure 1 discloses the axes of the bore of the piece and telescopic sight I5 as being in the same horizontal plane it is to be understood that such relationship of these axes is not essential to accomplish boresighting by the system herein disclosed. The axis of the telescopic sight I5 may be vertically displaced above or below the axis of the bore of the piece. In this latter case it is only necessary to orient the line 35 on the reticle of collimator 23 to be in a plane parallel to the plane containing the axis of the bore of the piece, which may be effected by any conventional means.

While I have described the diametral lines of the collimators being superposed upon the reticle of the telescopic sight I5 in intersecting relation it will be understood that each of the collimator lines-may be caused to pass through` a different ducial mark of the telescopic objective if preferred for reasons of the reference axes employed.

Having now fully describedv my invention I claim:

1. In a boresighting device for an artillery piece having an offset telescopic sight comprising a reticle, a first collimator having a normally verticalrveticmle, means mounting said rst collimator within the bore of 'said artillery piece adjacent the muzzle thereof and with its optical axis coincident with the bore axis, a chassis, means fixedly mounting said chassis on the muzzle of said artillery piece, a second collimator having a normally horizontal reticle, means mounting said second collimator on said chassis to establish a line which is a prolongation of the line of said offset telescopic sight and 'parallel with a verticalplane through the bore axis of said artillery piece, a prism located between said second collimator and said telescopic sight for transmitting the rays from the second collimator onto the field of view of said telescopic sight, and.' optical' reflectors xedly mounted upon said chassis to deect the rays from said first collimator linto substantial coincidence with the rays vof said second collimator and into superposed intersecting relationship with the ducial mark of said telescopic sight. v

2. The structure-ofmclai'm 1 wherein said opti-A cal reflectors comprise a first penta-prism arranged to deflect rays from said first collimator, a second penta-prism -arranged to transmit rays from said second collimator and having a smaller prism resting upon one face whereby said latte'i rays are transmitted into the eld of view of said telescopic sight withoutdeviation asv from a plate having plane parallel faces, said rays from said rst collimator being deflected into substantial coincidence with the rays of said second' lcol.- limator and into superposed intersecting relationship with a ducial mark upon the reticle o f said 4. The structure of claim 1 wherein said means provided for positioning the first collimator within said bore comprise spaced diaphragms nished Within tolerances to permit accurate tting Within the bore and provided with apertures to receive said first collimator whereby the axis of vsaid rstollimator may be made to coincide with a reference axis through the bore.

5. The structure of claim 1 wherein said means provided for positioning the rst collimator in said bore comprise spaced diaphragms having expanding shoes adapted to be radially expanded to engage the surface of the bore.

IRVINE C. GARDNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

